The best resource for home canning is the USDA Guide for Food Preservation or calling your Master Food Preserver at your local Extension Agent. These two resources will provide you with the most up-to-date information. Most recipes you will find online are USDA and anyone who does home canning will tell you only to use official tried recipes.
There are two types of canning: Water Bath Canning and Pressure Canning. Depending on what you are canning will depend which type you will do. A good rule of thumb is that fruits are mostly water bath canned because they have a higher acid content and vegetables are pressure canned because they have a low acid content. When you are dealing with low acid you need to take extra measures to ensure you will not have the botulism toxin in your food. Pressure Canning safe-guards against botulism.
When dealing with tomatoes always use the USDA guide. Their acid content is in the middle and your recipe will determine whether you should water bath can or pressure can.
As I mentioned on the other page (Garden Resources) it is also important to date your jars and put the expiration date on the jar as well. Just because you are canning doesn't mean the items will have an endless shelf life. Most items will last 2-3 years unopened; however, it is best to use the food within one year to maintain the best color and quality. A good rule of thumb is to can enough to last you until your next canning season.
Here are a few resources for preserving but like I mentioned before always check the USDA guide to make sure changes haven't been made since the previous year.
►Root Cellaring: Natural Cold Storage of Fruits and Vegetables
by Mike Buble
"Anyone can learn to store fruits and vegetables safely and naturally with a cool, dark space (even a closet!) and the step-by-step advice in this book."